1. Field of the Invention
The present invention relates to the field of electronic circuits; more specifically, it relates to a circuit that compensates for leakage current through a capacitor.
2. Background of the Invention
Dielectric leakage is a significant problem in the design of very precise analog and/or digital circuits. For example, when a P-channel field effect transistor (PFET) is used as a capacitor (PCAP) or when an N-channel field effect transistor (NFET) is used as a capacitor (NCAP) for the loop filter capacitor of a phase locked loop (PLL) circuit, leakage due to tunneling when the gate dielectric is less than 2.0 nm thick can cause the oscillator frequency of the PLL to drift between capacitor refresh cycles resulting in unacceptable jitter and reduced performance. Alternative schemes of using thick dielectric capacitors can introduce unwanted capacitor-voltage (C-V) curve distortions as well as increase die area and fabrication steps and thus increase fabrication time and cost. Therefore, a method for compensating leakage current through a capacitor in very precise analog and digital circuits is needed.